Fix PR 100925: Limit some a?CST1:CST2 optimizations to intergal types only

Fix PR 100925: Limit some a?CST1:CST2 optimizations to intergal types only

The problem here is with offset (and pointer) types is we produce
a negative expression when this optimization hits.
It is easier to disable this optimization for all non-integeral types
instead of finding an integer type which is the same precission as the
type to do the negative expression on it.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	PR tree-optimization/100925
	* match.pd (a ? CST1 : CST2): Limit transformations
	that would produce a negative to integeral types only.
	Change !POINTER_TYPE_P to INTEGRAL_TYPE_P also.

gcc/testsuite/ChangeLog:

	* g++.dg/torture/pr100925.C: New test.